Worldwide, gastrointestinal infections and diarrheal diseases result in significant morbidity and mortality with approximately four million deaths each year. The majority of infections occur in infants and children living in developing nations. Currently, the most common etiologic agents are the rotaviruses. More recently, the role for enteric adenoviruses, astroviruses, Norwalk virus and other caliciviruses in the pathogenesis of childhood diarrheal diseases has received further clarification. Each year, in developing nations, rotavirus infections result in approximately 870,000 deaths in children less than five years of age. In the United States rotavirus disease is estimated to cost over one billion US dollars per year. By the age of three, almost every child in the world is infected with rotaviruses. The purpose of this study is to describe the role of rotaviruses, enteric adenoviruses, astroviruses, and caliciviruses as causes of diarrhea in a population-based cohort of Egyptian children. This information should help in the development of preventive measures against infection by these viruses including the development and future evaluation of candidate vaccines. Since the start of this study, 2403 frozen stool specimens have been transported from our field site in Abu Homos, Egypt to the laboratory of Dr. Glass at the CDC. These specimens were collected over a one year period beginning in February 1995 from a cohort of approximately 200 children less than three years of age under active surveillance for diarrhea. These samples have all been screened by EIA for the presence of rotaviruses, enteric adenoviruses, and astroviruses. Preliminary screening found 62 specimens positive for rotaviruses, the most important cause of childhood diarrhea. Surprisingly, there were even more specimens positive for adenoviruses (80) and astroviruses (86). All positive samples are to be further characterized by G and P grouping for the rotaviruses and by serotype for the astroviruses. The characterizations and confirmations will be done using PCR and virus cultivation. In view of our preliminary findings, we will expand the diagnostic evaluations to include the specimens collected during the second year of follow-up of the same cohort of children. The availability of sequential serosurveys performed on the study cohort during the second year of follow-up will allow Dr. Glass to perform selective serologic assays to determine acquisition of antibody to astroviruses, rotaviruses, and four to five of the calicivirus genotypes. The latter should help determine which assays will be most useful when evaluating the stools for caliciviruses.